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Abstract
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Nanoindentation test was employed to measure the actual hardness and yield strength of the stir zone in the friction stirwelded
single-phase brass joints. For this aim, different joints were prepared according to an experimental matrix based on
the central composite rotatable design. In this design matrix, the tool rotational speed, tool traverse speed, and tool axial
force were the input parameters. The outputs were the hardness and yield strength of the joints. To measure the hardness
and tensile strength of the joints, the nanoindentation test was employed. Moreover, electron back scattered diffraction and
transmission electron microscopy techniques were used to study the microstructural features. The results showed that by
decreasing rotational speed and axial force, and by increasing the traverse speed, the hardness and yield strength of the
joints were increased. In other words, lower heat inputs caused higher strength in the joints. Finer grain sizes, larger grain
average misorientation amounts, i.e., existence of more dislocations, and greater Taylor factors in the lower heat input joints
revealed that the influence of grain boundaries, dislocations, and texture were the origins of better mechanical properties.
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